Junction field effect transistors, JFETs, can be fabricated using fabrication processes which are similar to, and compatible with, the processes used for the fabrication of bipolar transistors. For example a back gate (also known as bottom gate) of a JFET can be formed from the collector of a bipolar transistor. The drain and source are formed in the same fabrication step that is used to form the base region of the bipolar transistor.
JFETs can be formed as P channel or N channel devices. Ideally a FET would take no gate current. However real devices and especially N channel JFETs can enter regimes where the gate current rises significantly when the current density within the device is relatively large and the drain-source voltage of the device is relatively large. “Large” in this context varies from device to device and may only be a few volts or tens of volts.